Parvovirus Infections¶
Chapter 202 | Part 5: Infectious Diseases · Part 5 – Infectious Diseases: Viral (incl. HIV) · Chapter 202
Key Clinical Points¶
- B19V is an Erythroparvovirus with a narrow tropism for erythroid progenitors, causing transient erythropoiesis arrest.
- Erythema infectiosum (fifth disease) presents with a 'slapped-cheek' rash in children.
- Transient aplastic crisis (TAC) occurs in patients with increased erythropoiesis (e.g., hemolytic disorders).
- Pure red cell aplasia (PRCA) develops in immunocompromised patients without neutralizing antibodies.
- Diagnosis relies on IgM seroconversion or PCR; PCR alone is not diagnostic for acute infection due to long-term DNA persistence.
- Hydrops fetalis occurs in 10-20% of nonimmune hydrops cases with maternal infection before week 20.
- IVIG (400 mg/kg daily x5-10 days) treats TAC and PRCA; no antiviral drugs are available.
- B19V DNA persists in tissues for decades without causing disease in immunocompetent individuals.
- No approved vaccine exists.
- Rash recurrence with exercise or sunbathing does not indicate infectiousness.
1. DEFINITION & OVERVIEW¶
Parvovirus B19 (B19V) is a nonenveloped, icosahedral virus with a linear single-stranded DNA genome (~5000 nucleotides). It belongs to the genus Erythroparvovirus due to its narrow tropism for erythroid progenitors.
Definition (Harrison's 22e): B19V belongs to the genus Erythroparvovirus, so named due to its narrow tropism of erythrocyte precursors in the bone marrow.
1.1 Viral Structure & Genome¶
• Diameter: ~22 nm • Structure: Nonenveloped, icosahedral • Genome: Linear single-stranded DNA (~5000 nucleotides) • Host Range: Humans (B19V), various animals (AAVs, parv4, HBoVs, bufavirus, cutavirus)
1.2 Genotypes¶
• Genotype 1: Predominant worldwide • Genotype 2: Rarely causes active infections • Genotype 3: Most diverse; more common in western Africa
2. EPIDEMIOLOGY¶
B19V infects humans globally, with outbreaks in schools and day-care centers during winter/spring. Transmission occurs via the respiratory route before rash or arthralgia onset.
• Seroprevalence: 50% of children seropositive by age 15; up to 80% in elderly • Viral Load: Up to 10^14 particles/mL in immunocompromised individuals • Screening: Blood products are screened for B19V DNA
2.1 Seroprevalence Trends¶
• Genotype Distribution: Genotype 1 is the predominant strain.
2.2 Transmission Dynamics¶
• Route: Respiratory • Timing: Pre-rash/arthralgia onset • Settings: Schools, households, day-care centers • Viral Load: Up to 10^14 particles/mL in immunocompromised individuals
3. ETIOLOGY & PATHOPHYSIOLOGY¶
B19V replicates in erythroid progenitors via specific receptor interactions.
• Primary Receptor: N-terminal VP1u region • Secondary Receptor: Blood group P antigen (VP2) • Resistance: Individuals lacking P antigen are resistant.
3.1 Receptor Biology¶
• Primary Receptor: N-terminal VP1u region • Secondary Receptor: Blood group P antigen (VP2) • Timing: P antigen is required at a later intracellular step.
3.2 Pathogenesis Cascade¶
- Replication in erythroid progenitors
- High-titer viremia (10^4–10^12 particles/mL) →
- Cytotoxicity leading to erythropoiesis arrest →
- Viral load decline with persistent low-level DNAemia →
- IgM response (2–3 weeks) resulting in rash/arthralgia in immunocompetent individuals →
- Chronic infection in immunocompromised individuals resulting in PRCA.
4. CLINICAL FEATURES¶
Most infections are asymptomatic. Symptomatic presentations vary by host status:
• Erythema Infectiosum (Fifth Disease): Common in children; characterized by a 'slapped-cheek' facial rash followed by a lacy reticular pattern on the trunk and extremities. • Polyarthropathy Syndrome: Affects 50% of adults (more common in women); involves symmetrical joints (hands, wrists, ankles) for several weeks. • Transient Aplastic Crisis (TAC): Occurs in patients with increased erythropoiesis (e.g., hemolytic disorders, sickle-cell crisis). • Pure Red Cell Aplasia (PRCA): Occurs in immunocompromised patients (AIDS, transplant recipients). • Hydrops Fetalis: Occurs in 10–20% of nonimmune hydrops cases with maternal infection before week 20.
4.1 Erythema Infectiosum¶
• Clinical Presentation: 'Slapped-cheek' facial rash; progresses to lacy reticular pattern on trunk/extremities. • Prodrome: ~7–10 days before rash appearance. • Note: Rash recurrence with exercise or sunbathing does not indicate infectiousness.
4.2 Polyarthropathy Syndrome¶
• Demographics: 50% of adults; more common in women. • Presentation: Symmetrical joint involvement (hands, wrists, ankles). • Duration: Resolves within weeks; may recur for months. • Differential Note: May mimic rheumatoid arthritis (RF often present).
4.3 Transient Aplastic Crisis (TAC)¶
• Host Profile: Patients with increased erythropoiesis (e.g., hemolytic disorders, sickle-cell crisis). • Presentation: Severe anemia, low reticulocyte count. • Bone Marrow: Giant pronormoblasts and absence of erythroid precursors. • Diagnostic Marker: Reticulocytopenia in sickle-cell crisis is diagnostic.
4.4 Pure Red Cell Aplasia (PRCA)¶
• Host Profile: Immunocompromised patients (AIDS, transplant recipients). • Presentation: Persistent anemia, reticulocytopenia. • Serology: Low/absent IgG; high viral load (>10^12 IU/mL). • Bone Marrow: Scattered giant pronormoblasts.
4.5 Hydrops Fetalis¶
• Maternal Infection: Required before 20 weeks gestation. • Risk of Fetal Loss: ~9% if infected <20 weeks. • Characteristics: Gross edema, severe anemia; not teratogenic (rare CNS/ocular abnormalities).
5. DIFFERENTIAL DIAGNOSIS¶
Key clinical distinctions are required to differentiate B19V from other conditions:
• Rash Differentiation: Erythema infectiosum is clinically indistinguishable from other viral exanthems; serology is recommended for pregnant women. • Arthropathy Differentiation: Polyarthropathy may mimic rheumatoid arthritis (RF often present); note that B19V DNA in synovia does not prove causation.
5.1 Rash Differential¶
• Viral Exanthems: Clinical appearance of B19V rash is indistinguishable from other viral exanthems. • Recommendation: Confirm with serology in pregnant women.
5.2 Arthropathy Differential¶
• Rheumatoid Arthritis: Presentation may mimic RA (RF often present). • Caveat: Presence of B19V DNA in synovial fluid is not diagnostic for the cause of arthralgia.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnosis relies on serology and PCR to distinguish between acute infection and persistent viral presence.
• Serology: ◦ IgM: Detectable at rash onset or TAC day 3; persists ~3 months. ◦ IgG: Detectable by day 7; indicates immunity (avidity increases over 6 months). ◦ Acute Infection Criteria: Seroconversion OR ≥4-fold IgG increase over 2 weeks. • PCR & Viral Load: ◦ Acute Viremia: Defined as >10^12 IU/mL serum. ◦ Persistence: DNA remains detectable for months/years in healthy tissues; PCR alone is not diagnostic of acute infection. • Bone Marrow: ◦ TAC/PRCA: Identification of giant pronormoblasts and absence of erythroid precursors.
Table 202-1: Diseases Associated with Human Parvovirus B19 Infection and Methods of Diagnosis
| DISEASE | HOSTS | IgM | IgG | PCR | QUANTITATIVE PCR |
|---|---|---|---|---|---|
| Fifth disease | Healthy children | Positive | Positive | Positive | >10^4 IU/mL |
| Polyarthropathy syndrome | Healthy adults (more often women) | Positive within 3 months of onset | Positive | Positive | |
| Transient aplastic crisis | Patients with increased erythropoiesis | Negative/positive | Negative/positive | Positive | Often >10^12 IU/mL, but rapidly decreases |
| Persistent anemia/pure red cell aplasia | Immunodeficient or immunosuppressed patients | Negative/weakly positive | Negative/weakly positive | Positive | Often >10^12 IU/mL, should be >10^6 without treatment |
| Hydrops fetalis/congenital anemia | Fetuses (of mothers infected <20 weeks) | Negative/positive | Positive | Positive amniotic fluid or tissue | n/a |
6.1 Serology Details¶
• IgM: Detected by EIA at rash onset or TAC day 3. • IgG: Detectable by day 7; avidity increases over 6 months. • ETS EIA: Compares linear vs. conformational VP2 epitopes.
6.2 PCR & Viral Load¶
• Acute Viremia: >10^12 IU/mL serum. • Persistence: Detectable for months/years post-infection. • Tissue PCR: Not diagnostic (viral DNA persists in healthy individuals).
6.3 Bone Marrow Findings¶
• TAC/PRCA: Characterized by giant pronormoblasts and absence of erythroid precursors.
7. MANAGEMENT & TREATMENT¶
No antiviral drugs are available; management is focused on supportive care and specific immunomodulatory treatments.
- Symptomatic Management: • Erythema infectiosum: Self-limited; no specific treatment. • Polyarthropathy: Self-limited; IVIG not beneficial.
- Transient Aplastic Crisis (TAC) Treatment: • Primary options: Blood transfusions or IVIG (400 mg/kg daily x5-10 days). • Immunosuppressed patients: Consider temporary cessation of chemotherapy.
- Pure Red Cell Aplasia (PRCA) Treatment: • Therapy: IVIG (400 mg/kg daily x5-10 days). • Monitoring: Required for relapse surveillance.
- Pregnancy Management: • Screening: Screen seronegative mothers exposed to B19V. • Monitoring: Monitor pregnant women with positive results. • Intervention: Intrauterine transfusion for hydrops fetalis.
7.1 Symptomatic Management¶
• Erythema infectiosum: Self-limited; no specific treatment. • Polyarthropathy: Self-limited; IVIG not beneficial.
7.2 Transient Aplastic Crisis (TAC)¶
• Treatment: Blood transfusions or IVIG (400 mg/kg daily x5-10 days). • Immunosuppressed patients: Temporary chemotherapy cessation may help.
7.3 Pure Red Cell Aplasia (PRCA)¶
• Treatment: IVIG (400 mg/kg daily x5-10 days). • Monitoring: Relapse surveillance required.
7.4 Pregnancy Management¶
• Screening: Screen seronegative mothers exposed to B19V. • Monitoring: Monitor pregnant women with positive results. • Intervention: Intrauterine transfusion for hydrops fetalis.
8. PROGNOSIS & COMPLICATIONS¶
Prognosis varies significantly based on the host's immune status.
• Immunocompetent Hosts: ◦ Erythema infectiosum: Self-limited. ◦ TAC: Resolves with immunity. ◦ PRCA: Rare. • Immunocompromised Hosts: ◦ Chronic anemia develops without neutralizing antibodies. ◦ IVIG is effective for treatment. ◦ Persistent viral DNA remains in tissues.
8.1 Immunocompetent Hosts¶
• Erythema infectiosum: Self-limited. • TAC: Resolves with immunity. • PRCA: Rare.
8.2 Immunocompromised Hosts¶
• Chronic anemia: Develops without neutralizing antibodies. • IVIG: Effective for treatment. • Persistence: Persistent viral DNA in tissues.
9. SPECIAL CONSIDERATIONS¶
Key considerations include specific risks in pregnancy and complications in immunocompromised patients.
• Pregnancy: 30% fetal infection risk; ~9% fetal loss if infected <20 weeks. • Pediatrics: Erythema infectiosum common; polyarthropathy rare. • Immunocompromised: PRCA, chronic anemia, hemophagocytic syndrome.
9.1 Pregnancy¶
• Screening: Screen exposed seronegative mothers. • Monitoring: Monitor pregnant women with positive results. • Intervention: Intrauterine transfusion for hydrops fetalis.
9.2 Immunocompromised¶
• Conditions: AIDS, transplant recipients, lymphoproliferative disorders. • Treatment: IVIG, immunosuppression cessation.
10. KEY PEARLS & CLINICAL TRAPS¶
Critical pearls and pitfalls for clinical practice:
• Rash: Recurrence with exercise/sunbathing eq infectiousness. • PCR Limitation: PCR alone is not diagnostic of acute infection due to long-term DNA persistence in healthy tissues. • Synovial DNA: Presence of B19V DNA in synovia does not prove causation of arthralgia. • IVIG Utility: IVIG is effective for PRCA/TAC but NOT for erythema infectiosum or polyarthropathy.
10.1 Diagnostic Pitfalls¶
• PCR persistence: Viral DNA detectable for decades in healthy individuals. • Synovial DNA: Presence does not prove causation. • Rash differentiation: B19V rash indistinguishable from other exanthems.
10.2 Treatment Pearls¶
• IVIG: Effective for PRCA/TAC in immunocompromised; not effective for erythema infectiosum/arthropathy. • Transfusion: Required for TAC management.
Reference Tables¶
TABLE 202-1 Diseases Associated with Human Parvovirus B19 Infection and Methods of Diagnosis DISEASE Fifth disease…¶
Harrison's 22e, p.1524
| DISEASE | HOSTS | IgM | IgG | PCR | QUANTITATIVE PCR |
|---|---|---|---|---|---|
| Fifth disease | Healthy children | Positive | Positive | Positive | >104 IU/mL |
| Healthy adults (more often women) |
Positive within 3 months of onset |
Positive | Positive | ||
| Transient aplastic crisis | Patients with increased erythropoiesis |
Negative/positive | Negative/positive | Positive | Often >1012 IU/mL, but rapidly decreases |
| Immunodeficient or immunosuppressed patients |
Negative/weakly positive |
Negative/weakly positive |
Positive | ||
| Hydrops fetalis/ congenital anemia |
Fetuses (of mothers infected <20 weeks) |
Negative/positive | Positive | Positive amniotic fluid or tissue |
n/a |